Axis changeover apparatus

ABSTRACT

An axis changeover apparatus according to the invention changes axes of movement of a machine tool having axes with the same direction of movement, such as a cross rail axis and quill axis. A check is performed to determine the commanded strokes along axes (Z and W axes) from machining commands supplied by an NC command tape (1). If a move command has a commanded stroke which exceeds a set limit stroke value, the portion of the commanded stroke which exceeds the value is converted into a commanded stroke along the other axis having the same direction of movement, thereby elongating the apparent stroke.

BACKGROUND OF THE INVENTION

1. FIELD OF THE INVENTION

This invention relates to an axis changeover apparatus which, when amachine tool having a tool such as a cutter possesses a plurality ofaxes, controls the changeover of these axes.

2. DESCRIPTION OF THE RELATED ART

When a tool is moved and controlled based on command data from an NCcommand tape in an automatic lathe which performs turning work by meansof a tool such as an ordinary cutter, a stroke limit is set with regardto each axis of movement in such a manner that the tool will not collidewith a table or a tool rest.

The same is true for large-scale machine tools having a plurality ofaxes along the same direction of movement. These include multiple-axismachine tools in which the directions of movement of two axes, such asof a cross rail and quill, coincide with the direction of movement ofthe tool. In a case where machining is carried out by moving the tool asmall amount at a specific portion of a workpiece in such amultiple-axis machine tool, the quill axis is used. When a large amountof movement is made, as when changing a machined portion, the cross railis used.

In such a machine tool, there are many cases where the mechanicalarrangement is such that one axis rides on another. Moreover, it isnecessary to set an allowable value for the stroke of movement of eachaxis. Consequently, depending upon the program of the workpiece to bemachined, there are instances in which the amount of movement along anaxis of the tool in one machining step becomes too large and exceeds themovable stroke set for a specific axis. For example, when a machiningstep is programmed in which the movable stroke of the quill is exceeded,machining becomes impossible even if commands are issued. However,irrespective of the fact that the cross rail generally has the samedirection as the quill, the commands on the NC tape are created by beingdivided into commands for the quill axis and commands for the cross railaxis. Hence, commands are formed separately for the cross rail andquill.

Accordingly, not only must the programmer create a command tape whilebeing constantly aware of the allowable stroke set for each axis of themachine tool, but he must also form the commands separately for thecross rail and quill. As a result, only a program conforming to theallowable stroke values can be created. Further, this means that amachine tool in which the strokes of the cross rail and quill differcannot make use of a program, even if it has the same contents, that hasalready been created for another machine tool.

SUMMARY OF THE INVENTION

The present invention has been devised in order to solve these problemsand its object is to provide an axis changeover apparatus in which anaxis to be driven is automatically changed over, with respect to acommanded value exceeding an allowable stroke, between axes whosedirections of movement coincide.

According to the present invention, there is provided an axis changeoverapparatus for changing over axes to be driven when running by program amachine tool having a drive mechanism which drives a plurality of axesmovable in the same direction, comprising control means for controllingmovement of an axis having a large allowable stroke and an axis on thisaxis and having a small allowable stroke, these axes having movabledirections that are the same as each other, detecting means fordetecting that a commanded value to the control means has exceeded anallowable stroke set for a controlled axis, and converting means forconverting a portion of the commanded value that has exceeded theallowable stroke into a commanded value along the axis having the largeallowable stroke.

Accordingly, the axis changeover apparatus of the present invention issuch that when a commanded value regarding the axis having the shortmovable stroke exceeds the allowable stroke set for this axis inexecution of the contents of a machining command tape, a move commandcorresponding to the amount of excess can be outputted as a commandvalue for the axis having the long stroke. As a result, the apparentmovable stroke is elongated. This lightens the burden on the programmerwhen originating an NC machining command tape and makes it possible tomake common use of a machining command tape among a variety of machinetypes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an embodiment of the invention;

FIG. 2 is an explanatory view illustrating an example of an applicablemachine tool; and

FIG. 3 is a flowchart illustrating the operation of the embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the present invention will now be described in detailwith reference to the drawings.

FIG. 1 is a block diagram illustrating an example of the construction ofthe axis changeover apparatus of the present invention. By way ofexample, a plurality of drive mechanisms are controlled by a machiningcommand tape 1 regarding machining performed by a machine tool havingthe configuration shown in FIG. 2. This machine tool comprises a crossrail 13 supported by posts 11, 12 and having its up-and-down movementcontrolled by a W-axis drive mechanism, a Y-axis drive mechanism 14controlled to move transversely on the cross rail 13, and a quill axis(Z axis) 15 movable in the same direction as the W axis at the lower endof the Y-axis drive mechanism 14. The machine tool is such that aprescribed tool executes machining commands with respect to a workpiece16 by means of the quill axis 15.

Move commands along the respective axes of the machine tool are suchthat data from a machining command tape 1 read into an NC unit areapplied to a pulse distributor circuit 2 to be distributed along each ofthe W, Y and Z axes. Movement by the cross rail 13 in FIG. 2 correspondsto a large amount of movement when the distance from the tool to themachining surface is set to a predetermined value at high speed independence upon the size of the workpiece 16. A controlled variableregarding a comparatively small movement on the actual machining surfaceis set for the quill axis 15.

The pulse distributor circuit 2 is connected to a Z-axis output circuit41 and a W-axis output circuit 42 via a changeover circuit 3. Theseoutput circuits 41, 42 convert Z-axis distributed pulses IPL_(z) andW-axis distributed pulses IPL_(w) supplied thereto into drive commandswhich drive respective ones of the axis drive mechanisms 51, 52. Thepulse distributor circuit 2 is connected to a Z-axis detector circuit 61and a W-axis detector circuit 62. When required, a move command for thecross rail is formed from a portion of a Z-axis drive command, whichserves as a quill command value, in the changeover circuit 3, as will bedescribed later.

A Z-axis command position register 71 stores the present coordinate ofthe Z-axis drive mechanism 51, and a W-axis command position register 72stores the present coordinate of the W-axis drive mechanism 52. Theseregisters feed signals regarding position along the respective axes backto the detector circuits 61, 62. Limit values for each axis which arespecific to the machine tool are applied to the detector circuits 61, 62from a Z-axis stroke limit setting circuit 81 and a W-axis stroke limitsetting circuit 82. The detector circuit 61 performs monitoring todetermine whether the commanded value for the Z axis is within theallowable stroke. When the commanded value for the Z-axis exceeds theset limit value, the changeover circuit 3 converts the Z-axisdistributed pulses IPL_(z), which are to be converted into a commandedvalue for the W-axis drive mechanism 52, into W-axis distributed pulsesIPL_(w), so that movement of the tool corresponding to the amount ofexcess is implemented by the W-axis drive mechanism 52.

Thus, even if a move command regarding the workpiece 16 to be machinedis formed which exceeds the allowable stroke of the quill, the apparentallowable stroke along the quill axis 15 is elongated, thereby making itpossible to execute the machine program with flexibility. In addition,rather than separately forming the commands for the cross rail and quillfrom the start, it is possible to convert the commanded valuesautomatically when required. In consequence, machine tools of typeshaving different strokes can be controlled by the same command program.

FIG. 3 illustrates a control flow when command data distributed alongthe Z axis is converted into command data along the W axis in theapparatus of the above-described embodiment.

A distribution computation for the distributed pulses IPL_(z) commandedalong the Z axis is performed at the execution period of such processingas linear or circular interpolation regarding the position of the tool(step a). When a machine coordinate value ABS_(z) updated based on theresult of the computation is formed (step b), an OT check on the plusside is performed by the Z-axis detector circuit 61 based on a strokelimit signal OTP_(z) in the plus direction along the Z axis from thelimit value (step c). When the machine coordinate value ABS_(z) alongthe Z axis is greater than OTP_(z), distributed pulses IPL_(w) along theW axis are computed (step d). When the stroke limit value OTP_(z) is notexceeded, an OT check on the minus side is then performed (step e). Whenthe machine coordinate value ABS_(z) along the Z axis is smaller than astroke limit value OTM_(z) in the minus direction, a computation IPL_(w)=ABS_(z) -OTM_(z) for distributing pulses along the W axis in an amountequivalent to the excess over this value is executed (step f), andZ-axis distributed pulses IPL_(z) within the allowable stroke are outputto the Z-axis output circuit 42 (step g).

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the appended claims.

The axis changeover apparatus of the present invention is such that anaxis to be driven is automatically changed over, with respect to acommanded value exceeding an allowable stroke, between axes whosedirections of movement coincide. As a result, there can be provided anaxis changeover apparatus having many advantages in control of a machinetool, such as the ability to elongate apparent stroke and reduce thelabor involved in preparing a machining command tape.

What is claimed is:
 1. An axis changeover apparatus for changing overaxes to be program driven on a machine tool having a drive mechanism fordriving a plurality of axes in the same direction based on a commandedvalue, comprising:control means for controlling movement of a largestroke axis having a large allowable stroke and a small stroke axis,parallel to the large stroke axis, having a small allowable stroke;detection means for determining if the commanded value exceeds the smallallowable stroke; and conversion means for converting a portion of thecommanded value in excess of the small allowable stroke into achangeover command value along the large stroke axis having the largeallowable stroke.
 2. An axis changeover apparatus according to claim 1,wherein said conversion means comprises:pulse distributing means fordistributing commanded distributed pulses along a predetermined axis;and changeover means for changing over the distributed pulses exceedingthe allowable stroke.
 3. An axis changeover apparatus according to claim1, wherein the small stroke axis is a quill rail axis of the machinetool, and the large stroke axis is a cross rail axis of the machinetool.
 4. A method for changing over axes used to position a machine toolhaving a drive mechanism fordriving the machine tool along a largestroke axis and a small stroke axis, parallel to the large stroke axis,said method comprising the steps of:(a) distributing a command value toproduce movement of the machine tool along the small stroke axis; (b)determining if the command value exceeds a small allowable stroke of thesmall stroke axis; (c) producing, based upon said determining of step(b), a changeover command value for the large stroke axis by reducingthe command value by the small allowable stroke; and (d) producing,based upon said determining of step (b), a modified command value forthe small stroke axis by reducing the command value by the changeovercommand value.